Handling Orders from my new App

I am a bit new to app development, spent the last month or so doing an app that handles orders and I integrated the use of firebase as well as notification and apple pay.

Now once the payment is done from the app, how do i know what the order is and where do i receive the money, Do i need to create mote handling for that or does it automatically come from apply pay ?

Any pointers on this would be very helpful

Handling Orders from my new App
 
 
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